Oncostatin M is a secreted single-chain polypeptide cytokine that regulates the growth of certain tumor-derived and normal cell lines. A number of cell types have been found to bind the oncostatin M protein. See, for example, Linsley et al., J. Biol. Chem., 264: 4282 (1989). Oncostatin M has been shown to inhibit proliferation of a number of tumor cell types (Linsley et al. supra). In contrast, however, this protein has been implicated in stimulating proliferation of Kaposi's sarcoma cells (Nair et al., Science 255:1430, 1992; Miles et al., Science 255:1432, 1992; and Cai et al., Am. J. Pathol. 145:74, 1994).
Identifying and isolating oncostatin M-binding proteins, such as cell surface oncostatin M receptors, is desirable for such reasons as enabling study of the biological signal transduced via the receptor. Such receptors in soluble form also could be used to competitively inhibit a biological activity of oncostatin M in various in vitro assays or in vivo procedures. A soluble form of the receptor could be administered to bind oncostatin M in vivo, thus inhibiting the binding of oncostatin M to endogenous cell surface receptors, for example.
A protein known as gp130 has been found to bind oncostatin M, but with relatively low affinity (Gearing et al., Science 255:1434, 1992). Heterodimeric receptors comprising a leukemia inhibitory factor (LIF) receptor and gp130 bind oncostatin M with higher affinity than does gp130 alone, but also bind LIF with high affinity (Gearing et al., supra). For certain applications, a receptor that binds oncostatin M with high affinity, but that does not function as a high affinity LIF receptor, would be advantageous. Prior to the present invention, no such receptor had been identified or isolated.